The standard “Local Interconnect Network” (LIN) was developed as a specification for a serial communication system as a new de-facto standard in particular for inexpensive communication of intelligent sensors and actuators in motor vehicles. The LIN serves in particular for inexpensive communication and is based on a one-wire bus which can be associated with the field buses. The LIN is composed of a master device and one or more slave devices. The master device has knowledge about the temporal sequence of all data to be transmitted. Those data are transmitted by the corresponding slave devices when they are required to do so by the master device. That is effected by sending out a message header characterised by a given message address. Subsequently the slave device connects its data output to the bus.
The new LIN standard is also intended for communication between control devices and motor regulators for electric motors in motor vehicles. Thus for example voltages or currents in radiator cooling fan regulators and interior fan regulators are regulated by means of corresponding signals or messages by way of various interfaces like for example pulse width modulation (PWM) and LIN. In that case an LIN interface has the advantage of greater flexibility over a PWM interface as various messages can be communicated while the PWM interface can only deliver a signal frequency and a pulse duty cycle. In the case of the PWM interface, it was possible to achieve a certain degree of flexibility by a variation in the pulse duty cycle, for example between 0% and 100%.
FIG. 2 shows a diagrammatic time graph of a PWM signal in pulse form, showing the period duration T, the pulse duration tPD and the pulse pause tPP. In this case the frequency of the PWM signal occurs as the inverse of the period duration, that is to say f=1/T.
As many control systems are based on a PWM-based control there is a need for backward compatibility so that conventional PWM-based devices can communicate with more recent LIN-based devices, that is to say the information which can be transmitted by means of the LIN can also be transmitted by way of a PWM-interface.